Importance of space weathering simulation products in compositional modeling of asteroids: 349 Dembowska and 446 Aeternitas as examples

Abstract— Based on recent progress in simulating space weathering on asteroids using pulse‐laser irradiation onto olivine and orthopyroxene samples, detailed analyses of two of the A and R type asteroid reflectance spectra have been performed using reflectance spectra of laser‐treated samples. The visible‐near‐infrared spectrum of olivine is more altered than that of pyroxene at the same pulse‐laser energy, suggesting that olivine weathers more rapidly than orthopyroxene in space. The same trend can be detected from reflectance spectra of the asteroids, where the more olivine an asteroid has, the redder its 1 μm band continuum can become. Comparison of the 1 μm band continuum slope and the 2/1 μm band area ratio between the asteroids and olivine and pyroxene samples (including the laser‐treated ones) suggests that asteroids may be limited in the degree of space weathering they can exhibit, possibly due to the short life of their surface regolith. Their pyroxenes may also have a limited chemical composition range. Fitting the visible continuum shape and other parts of the spectra (especially the 2μm part) has been impossible with any combination of common rock‐forming minerals such as silicates and metallic irons. However, this study shows, for the first time, excellent fits of reflectance spectra of an A asteroid (Aeternitas) and an R asteroid (Dembowska), including their visible spectral curves, band depths and shapes, and overall continuum shapes. Our results provide estimates that Aeternitas consists of 2% fresh olivine, 93% space‐weathered olivine, 1% space‐weathered orthopyroxene, and 4% chromite, and that Dembowska consists of 1% fresh olivine, 55% space‐weathered olivine, and 44% space‐weathered orthopyroxene. These results suggest that space weathering effects maybe important to the interpretation of asteroid reflectance spectra, even those with deep silicate absorption bands. Modified Gaussian model deconvolutions of the laser‐irradiated olivine samples show that their identity as olivine remained. The most recent submicroscopic mineralogical analyses have revealed that the laser‐irradiated olivine samples contain nanophase iron particles similar to those in space‐weathered lunar samples.     

Seasonal barotropic sea surface height fluctuation in relation to regional ocean mass variation

A consistency between seasonal fluctuation of actual sea surface height (SSH) and those caused by mass and density variations in gyre-scale regions is examined. The SSH obtained from satellite altimetry (altimetric SSH) is adopted as the actual SSH. SSH caused by mass variation (mass-related SSH) is simulated using a barotropic global ocean model forced by water flux, wind stress and surface pressure. SSH caused by density variation (steric SSH) is calculated from water density profile, i.e. temperature and salinity profiles. The model SSH well represents mass-related SSH for gyre-scale regional means, and seasonal fluctuation of the altimetric SSH corrected for the model SSH is similar to that of steric SSH above a pressure level larger than 300 dbar. The results indicate that the mass-related SSH does not much respond to the baroclinic adjustment to the seasonally varying wind stress curl. The mass-related SSH forced by wind stress and surface pressure should be accounted for regional evaluation, though it is not necessary for global mean evaluation. Detection of steric SSH from altimetric SSH would be useful for assimilation approaches in which the altimetric SSH is treated as the variable reflecting subsurface temperature and salinity.     

Modeling interaction of fluid and salt in an aquifer/lagoon system

To simulate the dynamic interaction between a saline lagoon and a ground water system, a numerical model for two-dimensional, variable-density, saturated-unsaturated, and coupled flow and solute transport (saltwater intrusion by finite elements and characteristics [SIFEC]) was modified to allow the volume of water and mass of salt in the lagoon to vary with each time step. The modified SIFEC allows the stage of a lagoon to vary in accordance with a functional relation between the stage and water volume of the lagoon, and also allows the salt concentration of the lagoon to vary in accordance with the salt budget of the lagoon including chemical precipitation and dissolution of salt. The updated stage and salt concentration of the lagoon are in turn used as transient boundary conditions for the coupled flow and solute transport model. The utility of the modified model was demonstrated by applying it to the eastern Mediterranean coastal region of Turkey for assessing impacts of climate change on the subsurface environment under scenarios of sea level rise, increased evaporation, and decreased precipitation.     

Long-period ground motions from the 2003 Tokachi-oki earthquake

We study characteristics of long-period ground motions from the 2003 Tokachi-oki earthquake (Mj 8.0), a large interplate earthquake, based on spatial distribution maps and attenuation relationships for four kinds of peak ground velocity (PGV) value. The first kind (PGV(WB)) is obtained from a maximal value of vector sum of the three-component, wide-band velocity seismograms, and the other three kinds (PGV(BP10), PGV(BP20), and PGV(BP30)) are obtained from a maximal value of vector sum of the three-component, narrow band-pass filtered velocity seismograms (the central periods are 10, 20, and 30 s). The spatial distribution maps for all kinds of PGV value show azimuth dependence; the PGV values in Hokkaido, northern side of the epicenter are larger than those in Tohoku, southwestern side of the epicenter, when compared at a comparable distance. We find that the features result from the radiation pattern of long-period surface waves, that is, the source effect. The attenuation relationships show the following trends: The PGV(WB) values are larger than the sum of the PGV(BP10), PGV(BP20), and PGV(BP30) at distances (D) less than 200 km, while the PGV(WB) values are comparable to the sum of the PGV(BP20) and PGV(BP30) at D > 200 km. This indicates that the PGV(WB) values at D < 200 km are affected by ground motions with periods less than 10 s, while long-period surface waves mainly contribute to the PGV(WB) values at D > 200 km. The basin site effects generate a patchy pattern in the spatial distribution maps and a large scattering in the attenuation relationships for the PGV(WB) and PGV(BP10) values. Finally, we conclude that the PGV(WB) values from the 2003 Tokachi-oki earthquake are controlled by the radiation pattern of long-period S and surface waves and various basin site effects.     

Effect of temperature on the methyl chloride production rate in a marine phytoplankton, <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>

Methyl halides such as methyl chloride (CH₃Cl) are known to be important carriers of halogen from the ocean to the atmosphere, and the halogens they release into the stratosphere by photolysis catalyze ozone depletion. Marine phytoplankton have been reported as a source of CH₃Cl, but the effects of environmental temperature on the CH₃Cl production by phytoplankton have not been investigated. In this study, we investigated the effects of temperature on the production of CH₃Cl in the culture of a marine diatom, Phaeodactylum tricornutum CCMP 630, incubated at 10, 15, 20, 25, and 30 °C. CH₃Cl concentrations in cultured samples were determined using purge and trap gas chromatograph–mass spectrometry. Phytoplankton growth was monitored by measuring the chlorophyll a concentrations. CH₃Cl production was observed for several weeks at four different temperatures ranging from 10 to 25 °C. The CH₃Cl production from P. tricornutum was increased with increasing temperature from 10 to 25 °C, and the maximum production rate for CH₃Cl was 0.21~0.26 μmol (g chlorophyll a)^?1 d^?1 at 25 °C, which was several times higher than that at 10 °C (~0.03 μmol (g chlorophyll a)^?1 d^?1). The Arrhenius equation was successfully used to characterize the effects of temperature on the production rates of CH₃Cl in the culture of P. tricornutum. Our results suggest that water temperature directly affects CH₃Cl production derived from P. tricornutum and that water temperature would be a significant factor for estimating the emissions of CH₃Cl from marine environments.     

Petrochemistry of Volcanic Rocks in the Hishikari Mining Area of Southern Japan, with Implications for the Relative Contribution of Lower Crust and Mantle-derived Basalt

Abstract. This study presents the petrographical, mineralogical, and geochemical characteristics of Late Pliocene‐Pleistocene volcanic rocks distributed in the Hishikari gold mining area of southern Kyushu, Japan, and discusses their origin and evolution. The Hishikari volcanic rocks (HVR), on the basis of age and chemical compositions, are divided into the Kurosonsan (2.4–1.0 Ma) and Shishimano (1.7–0.5 Ma) Groups, which occur in the northern and southern part of the area, respectively. Each group is composed of three andesites and one rhyodacite. HVR are characterized by high concentrations of incompatible elements compared with other volcanic rocks in southern Kyushu, and have low Sr/Nd and high Th/U, Th/Pb, and U/Pb ratios compared with typical subduction‐related arc volcanic rocks. Modal and whole‐rock compositions of the HVR change systematically with the age of the rocks. Mafic mineral and augite/hypersthene ratios of the andesites decrease with decreasing age in the Kurosonsan Group, whereas in the Shishimano Group, these ratios are higher in the youngest andesite. Similarly, major and trace element compositions of the younger andesites in the former group are enriched in felsic components, whereas in the latter group the youngest andesite is more mafic than older andesites. Moreover, the crystallization temperature of phenocryst minerals decreases with younger age in the former group, whereas the opposite trend is seen in the latter group. Another significant feature is that rhyodacite in the Shishimano Group is enriched in felsic minerals and incompatible elements, and exhibits higher crystallization temperatures of phenocryst minerals than the rhyodacite of the Kurosonsan Group. Geochemical attributes of the HVR and other volcanic rocks in southern Kyushu indicate that a lower subcontinental crust, characterized by so‐called EMI‐type Sr‐Nd and DUPAL anomaly‐like Pb isotopic compositions, is distributed beneath the upper to middle crust of the Shimanto Supergroup. The HVR would be more enriched in felsic materials derived from the lower crust by high‐alumina basaltic magma from the mantle than volcanic rocks in other areas of southern Kyushu. The Kurosonsan Group advanced the degree of the lower crust contribution with decreasing age from 51 %, through 61 and 66 % to 77 %. In the Shishimano Group, the younger rhyodacite and andesite are derived from hotter magmas with smaller amounts of lower crust component (58 and 57 %) than the older two andesites (65 % and 68 %). We suggest that the Shishimano rhyodacite, which is considered to be responsible for gold mineralization, was formed by large degree of fractional crystallization of hot basaltic andesite magma with less lower crustal component.     

Assessing flood disaster impacts in agriculture under climate change in the river basins of Southeast Asia

Natural Hazards - This study focused on flood damage assessment for future floods under the impact of climate change. Four river basins of Southeast Asia were selected for the study. They included...     

Prediction of iodate adsorption and surface speciation on oxides by surface complexation modeling

Aqueous iodine species occur mainly as iodide (I⁻) and iodate (IO₃⁻), depending on redox conditions. The adsorption of IO₃⁻ on naturally occurring oxides under oxic conditions is of environmental concern. The adsorption behaviors of IO₃⁻ by hydrous ferric oxide (HFO), α-FeOOH, and γ-Al₂O₃ were examined in this study as functions of pH, ionic strength, and solid concentration. Adsorption data were analyzed using an extended triple-layer model (ETLM) for surface complexation modeling to infer IO₃⁻ adsorption reactions and equilibrium constants. Results of ETLM analysis suggest that adsorption of IO₃⁻ is both an outer-sphere and an inner-sphere process, as expressed by the following complexation reactions, which are consistent with the independent pressure jump kinetic results and adsorption enthalpy measurements

     

Granulite formation in a Gondwana fragment: petrology and mineral equilibrium modeling of incipient charnockite from Mavadi, southern India

We report a new occurrence of incipient charnockite from Mavadi in the Trivandrum Granulite Block (TGB), southern India, and discuss the petrogenesis of granulite formation in an arrested stage on the basis of petrography, geothermobarometry, and mineral equilibrium modeling. In Mavadi, patches and lenses of charnockite (Kfs?+?Qtz?+?Pl?+?Bt?+?Grt?+?Opx?+?Ilm?+?Mag) of about 30 to 220 cm in length occur within Opx-free Grt-Bt gneiss (Kfs?+?Qtz?+?Pl?+?Bt?+?Grt?+?Ilm). The application of mineral equilibrium modeling on the charnockite assemblage in the NCKFMASHTO system to constrain the conditions of charnockitization defines a P–T range of 800 °C at 4.5 kbar to 850 °C at 8.5 kbar, which is broadly consistent with the results from the conventional geothermobarometry (810–880 °C at 7.7–8.0 kbar) on these rocks. The P–T conditions are lower than the peak metamorphic conditions reported for the ultrahigh-temperature granulites from this area (T?>?900 °C). The heterogeneity in peak P–T conditions within the same crustal block might be related to local buffering of metamorphic temperatures by the Opx-Bt-Kfs-Qtz assemblage. The result of T versus mole H₂O (M(H₂O)) modeling demonstrated that the Opx-free assemblage in the Grt-Bt gneiss is stable at M(H₂O)?=?0.3 to 1.5 mol%, and orthopyroxene occurs as a stable mineral at M(H₂O) <0.3 mol%, which is consistent with the petrogenetic model of incipient charnockite related to the lowering of the water activity and stabilization of orthopyroxene through the breakdown of biotite by dehydration caused by the infiltration of CO₂-rich fluid from external sources. We also propose a possible alternative mechanism to form charnockite from Grt-Bt gneiss through slight variations in bulk-rock chemistry (particularly for the K- and Fe-rich portion of Grt-Bt gneiss) that can enhance the stability of orthopyroxene rather than that of biotite, with K-metasomatism playing a possible role.     

Geochemistry of caldera-forming and resurgent magmas in the Pliocene Hiwada caldera,northeast Japan: An example of a monotonous intermediate system

The 2.9-Ma Hotokezawa Ignimbrite, which was ejected from the Aizu caldera cluster in the northeast Japan arc, is a typical monotonous intermediate ignimbrite, with 40–50 vol% crystals and an eruptive volume of >140 km³ dense-rock equivalent. This ignimbrite filled Hiwada caldera and was deformed by post-caldera plutonic intrusions that formed a resurgent dome. The Hotokezawa Ignimbrite is a calc-alkaline, medium-K dacite to rhyolite with SiO₂ contents of 67.9–71.3 wt%, and has homogeneous trace-element abundances and Sr–Nd isotopic ratios. These geochemical features suggest that the Hotokezawa magma was formed by partial melting of amphibolitic crustal rocks. This crystal-rich magma did not appear during the post-caldera stage. Therefore, it is plausible that the chamber of eruptible magma was emptied by the caldera-forming eruption. In contrast, post-caldera plutonic rocks exhibit a variety of compositions and have a clear SiO₂ gap corresponding to the caldera-forming magma: the early pluton (tonalite) and later ones (quartz porphyry, granite porphyries, and granite) contain 62.0–66.6 and 71.2–76.5 wt% SiO₂, respectively. The tonalite and the Hotokezawa Ignimbrite form a continuous trend in their major-element variations. The Sr–Nd isotopic ratios of the ignimbrite and tonalite overlap, but those of the porphyries and granite are more enriched. The early tonalite represents the more basic part of the Hiwada caldera system that was held in small pockets separate from the main magma chamber, because its trace-element abundances are varied and distinct from those of the Hotokezawa Ignimbrite. The distinct compositional change from the Hotokezawa Ignimbrite to the late porphyries and granite indicates that the partial melting crust generating felsic magma was renewed by the subsequent intrusion of the mantle melts. The new felsic magma ascended through subsidence-related faults into the shallow caldera system and emplaced as laccoliths forming the resurgent dome.